Twist-drill.



0. PREDRIGK-SON.

' TWIST DRILL. APPLIGATIo-NFILED maso, 1907.

- 'Patented June A1, 1909.

lm@ SME@ MENT oFrio.

, v osera; riinnaionson, OF BUCHANAN, Miei-nein, AssieNos To cistron Toot COMPANY,

- f or cnicaeo, iLLiNois, A coa-PORATION or iLLiNois.

TWIST-DRXLL.

To vall whom it may concern:

- Be itlinown that'l', OSCAR Fnnnaioiison,

new 'and useful improvements in Twistlrills, of whichthe following is a specification, reference being had to the accompanying drawings.

My .invcntion relates to twist drills, and its object 1s to provide a drill which may be readily and firmly held in a suitable chuck and held true for drilling.

f is, usual in the manufacture of vtwist drills to provide a blanlf; which is rolled in 4thedorm of a long strip ot 4steel substantially lso it is then ground. must be between centers-that is to say, ydrill is put into the' grinding machine and rectangular in section and provided upon each oi? its two main parallel surfaces with a central longitudinal rib by -means of which l be held in chucks of the drill is adapted to well-linown form and construction. The drill'is then twisted so as to leave a portion f of the blank in its originalshape to forml a shank by which the drill may be held, and The grinding of the drill the isheld in that machiney betweencenters put into the two ends of the shank with a center' punch while the blank is still hot. The

" drill is soground, of course, that the edges of the twisted portion would lill a true. cylinder whose cross-sectionis a circlea' The 'point of the drill isthen sharpened and the 35 point must be coincident with thev mathematical central line ,ofthe cylinder. Upon the shank of the drill are left two projecting l' ribs. .ltis very A to have ythese ribs Stral line of symmetry of the drillthat is dilicult in forming the drill coincident with the cento say, with the line foi the cylinder which y' 'the twisted portion of the drill would lill, as

above'set 'forth-and even with the greatest I care in rolling ythey are apt to be a little out A'of the drill in such U tween chuck-blocks which would engage 1t hold it firmly and also l f of line, causing difficulties with the holding `oi`fthe drill in the chuck in proper and exact position for drilling. Owing also to the same diiculties in the formation of the drill it is very difficult to form the shank portion a way as ,to hold 1t beatits edges so as to in ,perfectly true drilling position. Todo sof it would be necessary that theehank portion of the drill should be in section an twisted lfromV a Patented Jane 1, 190e.

Application filed December 30, 1907. Serial lNo. 408,587.

exact parallelogram whose center should be the axis of symmetry of the. cutting portion of the drill and of which also the parallel faces should be parallel with the anis of rotation. the drill. It is obvious that it is very diilicult to iorm or grind these surfaces in such a way as to 'fulfil the above requirements. f f p Itis the object of my invention "to produce a ,drill which will obviate these dithculties vand which maybe used both in the ordinary' form of chucks which grasp the drill upon each side of its main parallel surfaces engaging the ribs thereof, and which may also be engaged by chuck-blocks `from its edges. 'lo accomplish this l. grind or iorin upon the shank of the drill, preferably while it is being ground, bevels upon each of the four edges of .the shank, which bevels shall be equidistant from theaxis of symmetry of the cutting surfaces of the drill or the axis oi' rotation of the drill, and which shall forni parts of the four sides of a par- 'allelograin whose center coincides with the axis of rotation of the drill, In other words, the diagonally opposite bevels are parallel with each other throughout their length and they axis of symmetry of the bevels corresponds with the axis of symmetry of the cutting surfaces ot thedrills. This may be readily done, as is above pointed out, while the drill isbeing ground.

Referring to the drawingsf-Figurel 'is a side' elevation of a drill, showing in dotted lines chuck-blocks engagingfits edges; Fig. 2 is a cross-section on lin-'efQ-Q of Fig. l; showing also `the chuck-blocks in dotted lines;` Fig. 3 is an enlarged. view, beingv a section through the shank of the drill, showing the parallelogram Jformed by its beveled edges.

4 indicates the shank of the drill and 5 the drill portion. l

6 indicates the cutting edge at the end oi the drill. t' The drill, as has been explained above, 1s bar of steel rolled in the forni of Va blank having longitudinal ribs .7, which are formed as closely as possible `.in the line of the axis of rotation of the drill, The drill isthen twisted, leaving the shank portion 4l, and ground as above described.

8-9 indicate bevels, which are ground, or otherwise ormed,'upon the four edges of the shank of the drill. As is best- 4*shown in Fig. 3, these edges form parts of the sides of a parallelograin indicated in dotted lines in Fig. 3, thel symmetric center of' which corresponds with the axis of rotation of the drill, or, in other words, the axis of symmetry of its cutting surfaces. As is also indicated in Fig. 3, these bevels are equidistant from the axis of rotation l0, the dotted lines a, b, c and Z being of equal length. The planes of the bevels 8 8 and 9-9, respectively, f are parallel to each other, as is shown by the dotted lines of the parallelogram in Fia. 3, and are also parallel throughout their length with the axis of rotation of the drill.

12 indicates in dotted lines a suitable form of chuck-block which may be used for engaging the bevelsin the shank of my drill and maybe supported, in and operated by any suitable chuck.

I am filing an application ot' even date herewith for Letters Patent of the United States for a new and impror d chuck containing chuck-blocks similar to those shown herein and adapted to operate them and support such a drill as I have above described. As such chuck and blocks are described in said application of even date herewith and as such chuck or block forms no part or my present invention, it is' believed that further description of them is unnecessary herein. It will be seen, however, from the above description that as long as the bevels are ground true, which may be readily and easily done as above pointed ont, the rest of the shank of the drill may be more or less ir regular and depart more or less from a true parallelogram in its several cross-sections, and its sides may vary somewhat from exact parallelism with their opposing sides and need not be ground perfectly straight and true, and the drill may still be held perfectly true for rotation and firmly and tightly in a. chuck.

One of the great advantages of my drill, as above described, is that it constitutes a drill which is able to be held by chucks adapted to grip its sides and hold it in position by means oit the longitudinal ribs, and which, at the same time, in cases where extreme accuracy is desired, may be held in chucks gripping 4it from its edges as above pointed l l I 1 out. TWhile it is true, as above pointed out, l

that it'is very difficult in the manufacture 0i these twist drills to get the longitudinal ribs in exact line with the center of rotation, still it may be done within a sulicient range of accuracy for many purposes in which extreme accuracy is not necessary; and this form of drill,-namely, the kind whose flat shank is engaged from its opposite sides by a suitable chuck holding it by means of the longitudinal ribspossesses many advantages where its use is possible. One of the advantages of holding the drill from its sides by a suitable chuck engaging the longitudinal ribs is that while accuracy may be slightly sacrificed a wide range of sizes of drills may be used in the same chuck, which may be a chuck of very simple construction. By forming, therefore, the drill shank as above described, with both the longitudinal ribs as accurately placed as possible and with the corners beveled as above set forth, a drill is formed which possesses both the advantages of the drill held by its sides by' longitudinal ribs and the advantages of ex treme accuracy when such accuracy is demanded.

That which I claim as my invention, and desire to secure by Letters Patent, is.-

l. A drill provided with a shank having four bearing corners forn'ied into bevels whose axis of symmetry coincides with the axis of rotation ot' the drill.

2. A drill provided with a shank having four bearing corners formed into bevels, the diagonally-opposite bevels being equidistant from the axis of rotation of the drill.

3. A drill having a shank quadrilateral in cross-section, the four corners ot' which are beveled, the axis of symmetry of said bevels coinciding with the axis of rotation of the drill.

4. A drill having a shank quadrilateral in cross-section, the four corners of which are beveled, the axis ot-synunctrv of said bevels coinciding with the axis ot rotation of the drill and parallel throughout their length to the said axis of rotation.

OSCAR FREDRICKSON. lVitnesses JOHN R. Lrrnvnr.. EUGENE B. Crank. 

